Vehicles having an electric powertrain are propelled using motor torque from one or more electric traction motors. The fraction motors draw electrical energy from a rechargeable energy storage system in electric vehicle (EV) drive modes, and when equipped with an internal combustion engine can selectively regenerate the energy storage system using engine torque as well as regenerative braking. The multiple rows of battery cells in a typical energy storage system generate heat during EV drive operation or when powering onboard electrical systems. As a result, thermal management systems are used to regulate temperature, with a typical thermal management system including various coolant loops through which coolant is circulated via a coolant pump.
Traditionally, a three-way cabin heater valve or CHV is used as part of any thermal management system in order to control the flow of coolant to and from a cabin heater core. Additionally, air is directed through ductwork across the heater core at a level regulated via a motor-driven heater flap. Hybrid and battery electric vehicles also use a high-voltage electric heater (HEH) to supply the necessary cabin heat for passenger comfort at times when engine coolant temperature remains relatively low, for example during extended EV drive modes.
A CHV is ordinarily switched to a first position to fluidly connect the cabin heater core to an engine coolant loop in what is referred to as an Engine Link mode, and to a second position to bypass the engine coolant loop in an Engine Bypass mode, with the latter mode typically used to manage an engine warm-up process. In the Engine Bypass mode, engine waste heat is not readily available for cabin heating and/or there is abundant electric energy available for the HEH to run at a higher output capacity such that fuel consumption and vehicle emissions are minimized. Engine Link mode, on the other hand, allows for utilization of available engine waste heat and enables the engine alone or both the engine and the HEH to supply any required cabin heating.